A conventional hinged-lid chocolate box comprises a parallelepiped-shaped tray for housing the chocolates (normally on a support with a seat for each chocolate) and having an open top end; and a ‘flat’ lid hinged to the tray along a hinge to rotate, with respect to the tray, between an open position and a closed position opening and closing the open top end respectively.
Because the chocolates are arranged in one layer, so they are all visible when the lid is opened, the tray has a large area and is low in height. As a result, the lid is also large, and, to ensure sufficient stiffness (i.e. prevent it from bending when opened) must be made thick (e.g. by superimposing and gluing together two, three or even four panels), this ‘wasting’ packing material.
To make a thin lid (and so save on packing material) without impairing its stiffness, it has been proposed to provide the lid with hollow peripheral ribs (i.e. running along the three free edges of the lid). The ribs normally have a triangular cross section and, being box-shaped, provide for considerable stiffness using very little packing material.
On conventional packing machines, however, folding the rigid blank along the perimeter of the lid to form the hollow ribs poses problems by frequently resulting in irregularly shaped ribs which, though structurally acceptable (even if not perfect), are totally unacceptable in terms of appearance (on account of the ribs being clearly visible when the lid is opened).
Patent Application EP1873070A1 describes a folding method and device for folding a flat blank into a parallelepiped-shaped container with four vertical hollow ribs along the four vertical edges.